The present invention broadly relates to a method and apparatus for reporting dangerous or other desired conditions and, more specifically, pertains to a new and improved method and apparatus for transmitting signals in an alarm system.
Generally speaking, the method of the present invention for signal transmission and signal processing in an alarm system comprising a central signal station and remotely located detectors is intended to be employed in a system in which the central signal station transmits an interrogation signal to the detectors and the detectors transmit response or status signals back to the central signal station after receiving the interrogation signal and with a time delay characteristic of each individual detector, the response signals corresponding to the current state of the individual detector and the central signal station receiving and evaluating the response signals.
The apparatus of the present invention relates to a device for reporting danger or other desired conditions which comprises a central signal station and remotely located detectors, in which the central signal station further includes a signal transmitter for transmitting interrogation signals and each of the detectors further includes a signal receiver for receiving the interrogation or scan signals, a signal transmitter for transmitting response or status signals, a sensor for influencing the response or status signals and delay means for temporally delaying the transmission of the response or status signals in relation to the reception of a interrogation signal by different delay times characteristic of each individual detector. The central signal station further includes a signal receiver for receiving the response or status signals transmitted by the individual detectors.
The detectors or danger reporting devices can be constructed to respond to the conditions to be expected and to be reported for a given application and may comprise corresponding sensors, sensitive for instance to fire, smoke, flames or prescribed gases or also to intrusion and theft.
Such methods and apparatuses are known, for instance from the German patent No. 2,533,330. They permit the determination of the source of the response signal and the location of the detector from the delay time of the response signal. They also permit the determination of the presence and the degree of a dangerous condition, such as the density of smoke, from the temporal duration of the response signal.
Such methods and apparatuses have the disadvantage that only the two parameters mentioned are available for signal transmission and therefore further information desired in the central signal station from the detectors cannot be transmitted without additional measures. The operational readiness and the correct functioning of the detector can therefore not be determined in the central signal station in this manner and the alarm system can give false alarms or unexpectedly fail to function.
A further disadvantage of such known devices is that the detectors have a relatively high energy consumption. When transmitting signals through electrical conductors, sufficient power for the energy supply of the individual detectors connected to the central signal station by the conductors is usually available. When a great number of detectors is connected to the central signal station in parallel by the same conductors or lines, as is often required in practice, the currents and the energy losses in the conductors can, however, assume values which make it difficult to assure a uniform energy supply for all detectors and such is no longer guaranteed.
Difficulties of this kind can be avoided by transmitting the signals in wireless communication, e.g. by means of electromagnetic radiation, such as radio waves or infrared radiation or by means of ultrasonic signals. The energy supply of the individual detectors is then usually provided by batteries in each detector. In order to attain the greatest possible longevity of such batteries and to assure a long-term operational readiness of such an alarm system of at least one year, the energy consumption of the detectors must be kept to a minimum and it is essential to monitor the operational state of the battery and thereby the functional state of the individual detectors continually and automatically in the central signal station. Defects must be located immediately and remedied. Hitherto known alarm systems cannot do this or have only a limited capacity to do so.